In a mechanical system such as a machine tool or a robot, the rotating direction and the rotation speed of a motor are controlled, so that the position, the speed, the number of revolutions, and the like of an control target to be controlled are controlled. A numerical control device normally generates a command value relating to, for example, the position and the speed at regular time intervals, and a motor control device receives this command value and controls, for example, the rotating direction, and the rotation speed of the motor. As a result, the control target moves to the designated position at the designated speed. The motor control device also receives feedback data relating to the motor drive current and the position and the speed of the control target, and transmits the feedback data to the numerical control device. By performing feedback control using the feedback data, the numerical control device generates command values for the next and subsequent cycles. In this manner, so-called servo control is performed in a mechanical system such as a machine tool or a robot.
Meanwhile, a mechanical system such as a machine tool or a robot is required to control a control target with high accuracy and at high speed. To increase the processing speed and the control accuracy, the processor of the numerical control device should perform more operations per unit time. In addition to the conventional servo control, furthermore, adaptive control, which detects temperature, humidity, and vibration of the control target, and the like with sensors and changes a command value or issues an additional command value in accordance with the sensor-detected results, is performed in order to perform more accurate control. Examples of the adaptive control include: correcting thermal displacement at a machine edge or a tool edge by using a result of detection performed by a temperature sensor; suppressing chatter vibration suppression by using a result of detection performed by an acceleration sensor; and preventing collision by using a result of detection performed by a vision sensor. Performing such adaptive control increases the load on the processor of the numerical control device.
Patent Literature 1 discloses a technique for reducing the load on a host controller, as a technique for avoiding an increase in the load on the processor of a numerical control device. According to this technique, a plurality of communication controllers provided under and connected in a tree structure to a host controller equivalent to a numerical control device, and motor control is shared between the host controller and communication controllers so that the load on the host controller is reduced.